/**
* @author AlbertDarren
* @contact 2563491540@qq.com
*/
#include <iostream>

using namespace std;

int main_15()
{
    int a,b,c;
    scanf("%d%d%d",&a,&b,&c);
    printf("%.3f\n",(float)(a+b+c)/3);
	return 0;
}
